Methods and systems for assisted direct start control

ABSTRACT

Methods and systems are provided for controlling a vehicle engine coupled to a stepped-gear-ratio transmission. One example method comprises, in response to a first vehicle moving condition, shutting down the engine and at least partially disengaging the transmission while the vehicle is moving; and during a subsequent restart, while the vehicle is moving, starting the engine using starter motor assistance and adjusting a degree of engagement of a transmission clutch to adjust a torque transmitted to a wheel of the vehicle.

FIELD

The present application relates to methods and systems for controllingan engine shut-down and a subsequent restart.

BACKGROUND AND SUMMARY

Vehicle engines may be configured to shut-off during idle conditionswhen the vehicle comes to a stop while a brake is applied and restartedonce the brake is released (e.g., a stop/start system). Such stop/startsystems enable fuel savings, reduction in exhaust emissions, reductionin noise, and the like. Fuel consumption may be further reduced byshutting down the engine before braking, for example, during extendedcoasting periods.

One example approach to shut-down and subsequently restart the enginewhile the vehicle is traveling is disclosed by Ries-Muller in U.S. Pat.No. 6,951,525. Therein, when the vehicle is moving with the operatorfoot off the accelerator and the brake pedal not applied (that is, thevehicle is coasting), the engine is shut-down and the transmissionclutches are disengaged to interrupt the engine braking torque. During asubsequent restart, the engine is restarted prior to a transition fromfree-wheel mode to engaged clutch travel mode by employing the fuelinjection system using a charge regulator and/or an electric motor.After the engine is restarted, the reference describes using acombination of a braking intervention and a clutch intervention tomaintain a vehicle braking torque during the transition, and therebyreduce undesirable vehicle deceleration when the vehicle speed is belowa threshold.

However, in this approach, when the vehicle is restarted while thevehicle is still moving, the combination of the wheel torque from themoving vehicle and the engine torque from the spinning engine may leadto a torque surge and the vehicle may lurch forward when a clutch issuddenly engaged. As such, this may degrade the quality of the restart.

Thus in one example, some of the above issues may be addressed by amethod for controlling a vehicle engine, the engine being coupled to astepped gear ratio transmission. In one embodiment, the methodcomprises, in response to a first vehicle moving condition, shuttingdown the engine and at least partially disengaging the transmissionwhile the vehicle is moving; and during a subsequent restart, while thevehicle is moving, starting the engine using starter motor assistanceand adjusting a degree of engagement of a transmission clutch to adjusta torque transmitted to a wheel of the vehicle. The method may furthercomprise, in response to a second vehicle moving condition, not shuttingdown the engine.

In one example, the first vehicle moving condition may include acoasting condition wherein the vehicle is moving and the vehicleoperator has not depressed the accelerator pedal or the brake pedal, andthe vehicle speed is above a threshold. In response to the coastingcondition, the engine may be shutdown, for example, by shutting off afuel supply to the engine. Then, the vehicle transmission may be atleast partially disengaged. In one example, the transmission may befully disengaged. In another example, the transmission may be partiallydisengaged and a transmission clutch may be slipped controllably. Forexample, a smaller amount of clutch slippage may be provided, the amountadjusted responsive to the vehicle speed and/or engine speed at the timeof engine shutdown.

During a subsequent restart, while the vehicle is still moving, and withthe transmission clutch still engaged, the engine may be started byactivating a starter motor, and a degree of engagement of thetransmission clutch may be adjusted, for example by engaging the clutchand controllably slipping the clutch, to adjust a torque transmitted tothe wheel. For example, a larger amount of clutch slippage may beprovided, the amount adjusted responsive to the vehicle speed and/orengine speed at the time of engine restart.

In this way, an engine may be restarted with starter motor assistancewhile the vehicle is still moving, and without transmitting the enginetorque to the wheels. By reducing the amount of engine torquetransferred to the wheels and added to the wheel torque, a smoothertransition between engine combusting and non-combusting modes may beachieved. Further, potential vehicle lurches from a sudden clutchengagement may also be reduced. As such, this may substantially improvethe quality of engine restarts. Similarly, by reducing the amount ofwheel torque that is transmitted from the wheels of a coasting vehicleto the engine following engine shutdown, a faster engine spin-down maybe achieved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a vehicle illustrating variouspower-train components.

FIG. 2 shows schematic diagram of an engine.

FIG. 3 shows a flow chart illustrating a control routine for an engineduring coasting conditions.

FIG. 4 shows a map graphically illustrating example engine shut-down andrestart operations during vehicle coasting, according to the presentdisclosure.

DETAILED DESCRIPTION

The following description relates to a method for controlling aninternal combustion engine coupled to a stepped gear ratio transmissionin a motor vehicle, such as in the vehicle system of FIG. 1. Duringvehicle coasting conditions (for example, when the accelerator pedal isnot pressed, and the brakes are not applied), an engine may be turnedoff and allowed to spin-down to rest while the vehicle is traveling. Asdescribed herein, in some embodiments, the transmission may bedisengaged (for example, partially disengaged) and the clutches may beslipped while the engine is shut down to reduce the wheel torque torqueapplied on the engine by the moving wheels. The transmission may then bemaintained in gear until and during a subsequent restart request. Duringthe restart, while the engine is cranked with a starter and while thevehicle is still traveling, the engagement of the transmission may beadjusted using a controlled slip of a transmission clutch. For example,an amount of clutch slippage may be increased at restart until theengine speed reaches a threshold, following which the amount of clutchslippage may be reduced. An engine controller may be configured toperform a control routine, such as the routine of FIG. 3, to adjust anamount of clutch slippage and an engagement state of the transmissionclutch(es), during engine shut-down and restart operations, responsiveat to at least an engine speed and/or vehicle speed during vehiclecoasting. Example adjustments are graphically depicted in FIG. 4. Inthis way, during an engine restart, clutch engagement may be rapidly andsmoothly performed, thereby improving the quality of vehicle restarts.By extending the duration of engine shut-down to conditions of vehiclecoasting, additional fuel economy benefits may be achieved.

Referring to FIG. 1, internal combustion engine 10, further describedherein with particular reference to FIG. 2, is shown coupled to torqueconverter 11 via crankshaft 40. Torque converter 11 is also coupled totransmission 15 via turbine shaft 17. In one example, transmission 15 isa stepped-gear ratio transmission. Torque converter 11 has a bypassclutch (not shown) which can be engaged, disengaged, or partiallyengaged. When the clutch is either disengaged or being disengaged, thetorque converter is said to be in an unlocked state. Turbine shaft 17 isalso known as transmission input shaft. In one embodiment, transmission15 comprises an electronically controlled transmission with a pluralityof selectable discrete gear ratios. Transmission 15 may also comprisesvarious other gears, such as, for example, a final drive ratio (notshown). Alternatively, transmission 15 may be a continuously variabletransmission (CVT).

Transmission 15 may further be coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23. Note that in oneexample embodiment, this power-train is coupled in a passenger vehiclethat travels on the road. While various vehicle configurations may beused, in one example, the engine is the sole motive power source, andthus the vehicle is not a hybrid-electric, hybrid-plug-in, etc. In otherembodiments, the method may be incorporated into a hybrid vehicle.

FIG. 2 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. Engine 10 may be controlled at least partially by a controlsystem including controller 12 and by input from a vehicle operator 132via an input device. In one example, the input device includes anaccelerator pedal 132 and a pedal position sensor 134 for generating aproportional pedal position signal PP. In another example, the inputdevice includes a transmission lever 136 that may be shifted betweendifferent gear options by the driver based on a desired transmissionoutput. In one preferred embodiment, the driver may have the followingdriver selectable options: park (P), reverse (R), neutral (N), driver(D), and low (L). In the depicted embodiment, the lever is known as aPRNDL lever, corresponding to the different options. In one example,when in park or neutral, substantially no torque may be transmitted fromthe engine to the transmission output. In drive, an electroniccontroller can control the transmission to select any available forwardgear ratios. In reverse, a single reverse gear is selected. In low, onlya lower set of forward gear ratios can be selected by the electroniccontroller. In some embodiments, there may be a low 1 and low 2 option.Transmission lever 136 may be located on a steering column or betweendriver and passenger seats.

Combustion chamber 30 of engine 10 may include cylinder walls 32 withpiston 36 positioned therein. Piston 36 may be coupled to crankshaft 40so that reciprocating motion of the piston is translated into rotationalmotion of the crankshaft. Crankshaft 40 may be coupled to at least onedrive wheel of a vehicle via an intermediate transmission system.Further, a starter motor may be coupled to crankshaft 40 via a flywheelto enable a starting operation of engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.Exhaust camshaft 53 operates exhaust valve 54 in accordance with theprofile of a cam located along the length of the exhaust camshaft.Intake camshaft 51 operates intake valve 52 in accordance with theprofile of a cam located along the length of the camshaft. Exhaust camposition sensor 57 and intake cam position sensor 55 relay respectivecamshaft positions to controller 12. Pump 72 supplies oil to indexintake camshaft 51 and exhaust camshaft 53 relative to crankshaft 40based on commands to camshaft actuators (not shown) supplied bycontroller 12. Pump 72 may be electrically driven so that camshafts maybe indexed when engine 10 is not rotating.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someembodiments, combustion chamber 30 may alternatively or additionallyinclude a fuel injector arranged in intake manifold 44 in aconfiguration that provides what is known as port injection of fuel intothe intake port upstream of combustion chamber 30.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP. Intake passage 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, during operationof engine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read-onlymemory 106 in this particular example, random access memory 108, keepalive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; vehicle brake121; a profile ignition pickup signal (PIP) from Hall effect sensor 118(or other type) coupled to crankshaft 40; throttle position (TP) from athrottle position sensor; and absolute manifold pressure signal, MAP,from manifold pressure sensor 122. Engine speed signal, RPM, may begenerated by controller 12 from signal PIP. Manifold pressure signal MAPfrom a manifold pressure sensor may be used to provide an indication ofvacuum, or pressure, in the intake manifold. Note that variouscombinations of the above sensors may be used, such as a MAF sensorwithout a MAP sensor, or vice versa. In one example, sensor 118, whichis also used as an engine speed sensor, may produce a predeterminednumber of equally spaced pulses every revolution of the crankshaft.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by microprocessorunit 102 for performing the methods described below as well as othervariants that are anticipated but not specifically listed.

Controller 12 also receives signals from and provides control signals toa transmission (not shown). Transmission signals may include but are notlimited to transmission input and output speeds, signals for regulatingtransmission line pressure (e.g., fluid pressure supplied totransmission clutches), and signals for controlling pressure supplied toclutches for actuating transmission gears.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Now turning to FIG. 3, a control routine 300 is illustrated forcontrolling an engine during vehicle coasting conditions. Specifically,routine 300 identifies opportunities while the vehicle is moving duringwhich combustion in the engine may be deactivated by a driver. Theroutine further modulates one or more transmission clutches to enable asmooth transition during a subsequent engine restart, while the vehicleis still moving.

At 301, the routine may determine whether the vehicle operator has moveda transmission lever (such as PRNDL lever of FIG. 2) from a driveposition (e.g., position D) to a neutral position (e.g., position N). Inone example, a driver may shift the lever from a drive position to aneutral position to allow the vehicle to coast with the engine off.Thus, by shifting from drive to neutral, the operator may manuallyover-ride inferred engine shutdown commands, such as automaticallyinferred engine shutdown commands responsive to extended coastingconditions elaborated herein below. If the driver has shifted the leverto the neutral position, then in response to a vehicle moving conditionwherein the vehicle is moving with a transmission lever in a neutralposition, the routine may proceed to 310 wherein an electroniccontroller may stop the engine with the transmission engaged and with afirst amount of transmission clutch slippage. In one example, aselaborated below, the engine may be stopped by shutting off a fuelsupply to the engine. In an alternate embodiment, in response to thedriver shifting the lever to the neutral position, the electroniccontroller may shutdown the engine with the transmission disengaged.

If the driver has not shifted the transmission to neutral, then at 302,extended coasting conditions may be confirmed. For example, vehiclecoasting may be inferred when the brake and accelerator pedals are notpressed and the vehicle is moving. If extended coast conditions are notconfirmed, the routine may end. Upon confirmation of vehicle coasting,at 304, entry conditions for a vehicle coast shut-down may be confirmed.Entry conditions may include, but are not limited to, engine purgingconditions, a charge state of a vehicle battery, engine temperature,emission control device temperature, etc. For example, the battery maybe employed to run various components (e.g., electric motors, lights,etc.) while the engine is off; thus, the engine may not be shutdownunless the battery attains a certain amount of charge. If entryconditions are not met, engine operation may be maintained at 306, thatis, the engine may not be shutdown.

If entry conditions are met, then at 308, the vehicle speed may beestimated and it may be determined whether the vehicle speed (VS) isabove a threshold value. In one example, the threshold speed may reflecta speed below which a vehicle coast shut-down operation may notsubstantially improve the vehicle's fuel economy. In another example,the threshold speed may correspond to an amount of vehicle inertia thatmay not be able to sustain vehicle coasting for a substantial duration,and wherein a potential vehicle stall may be imminent. Thus, if thevehicle speed is below the threshold, routine 300 may return to 306 tomaintain engine operation and not shutdown the engine.

If vehicle speed is at or above the threshold, then at 310, the enginemay be shutdown. In one example, a deceleration fuel shut-off (DFSO)operation may be executed to shut-off a fuel supply to the engine whilethe engine continues to rotate. Specifically, upon initiation of a DFSOoperation, fuel injection is cut-off to the cylinders. The engine thencontinues to rotate, due to transmission of torque from the vehicle'swheel(s) to the engine through an engaged gear of the transmission, forexample. Additionally at 310, a transmission clutch control operationmay be executed to adjust the wheel torque applied on the engine.Specifically, during the transmission clutch control operation, one ormore transmission clutches, including, for example, a torque converterlock-up clutch and/or a forward clutch, may be modulated to adjust atorque applied on the engine.

In one example, a torque converter lock-up clutch may be at leastpartially disengaged while the vehicle is moving to reduce the amount ofwheel torque transmitted from the vehicle's moving wheels to theshutdown engine. An engine controller may keep the torque converterlock-up clutch partially disengaged (and thus, also partially engaged),and then controllably slip the clutch. For example, the clutch may beslipped by a first (smaller) amount, the amount of slippage adjustedbased on, for example, engine speed and/or vehicle speed at the time ofengine shutdown. In an alternate example, the torque converter lock-upclutch may be fully disengaged.

In this way, during a first vehicle moving condition, when the vehicleaccelerator pedal and brake pedal are not being depressed, and thevehicle speed is above a threshold, the engine may be shutdown and thetransmission may be at least partially disengaged while the vehicle ismoving. In comparison, during a second vehicle moving condition, whenthe vehicle accelerator pedal and brake pedal are not being depressed,and with the vehicle speed being below the threshold, the engine may notbe shutdown. By turning off the engine while the fuel injectors areshut-off and while the operator's foot is off the accelerator pedal andbrake pedal, the amount of air pumped into the catalytic converter ofthe vehicle system's emission control device may be reduced. As such,this reduces the need for post fuel shut-off enrichment, therebyproviding additional fuel economy benefits.

At 312, it may be determined whether a restart is requested. The enginerestart may be initiated by a throttle or torque demand, by a change invehicle speed, by a vehicle speed that is above or below a threshold, bya change in brake position, or by other restart conditions. Further,numerous embodiments are anticipated under which different conditionsmay be used to determine whether or not the engine is to be restarted.In one embodiment, an engine restart is initiated when the vehicle speedis below a first threshold, the threshold representative of a firstvehicle inertia below which a coasting operation may not be sustained.In another embodiment, the brake position (e.g., the position of thevehicle brake pedal) and vehicle speed may be used to determine when torestart the engine. For example, if the operator's foot remains off thebrake, an engine at rest may stay at rest until the vehicle comes to astop and/or the operator presses his or her foot on the brake. Further,a change in position of the brake pedal (e.g., the brake pedal isrepositioned) may be used to initiate an engine start. In anotherembodiment, an engine restart may be initiated based on a rate of changein vehicle speed. For example, if the operator's foot is off the brakeand the vehicle is slowing because the road grade is changing (forexample, when the vehicle is travelling on an uphill track), the enginemay be restarted. Further, different signals and combinations of signalsmay be used to determine whether to restart the engine at 312.

If a restart is not requested, then at 314, the engine may remainshutdown and the partially disengaged state of the transmission may bemaintained, for example, by maintaining the engagement state and/orclutch slippage of the transmission clutch. If restart conditions areconfirmed, at 316, the engine may be started using starter motorassistance to initiate engine cranking.

In one example, the engine controller may be configured to communicatewith a navigation device (for example, a global positioning system,GPS). The navigation device may be configured to detect upcoming stopsigns and/or traffic lights. The navigation device may detect anupcoming vehicle stop based on various inputs, for example, from avehicle camera, a vehicle smart cruise system, a vehicle to trafficsignal communication system, a GPS with a map, etc. In one example,based on the indication (or prediction) of an upcoming vehicle stop, theroutine may be configured to not restart the engine in response to theoperator pressing the brake pedal and/or the vehicle speed droppingbelow a threshold. Additionally, the engine may be maintained in theshutdown condition for a threshold time following the operator pressingthe brake pedal. That is, the routine may enable the vehicle to continuecoasting to a complete stop and may extend the period of fuel injectionshut-off. In another example, the navigation device may include a gradedetection system configured to provide an estimate of the track grade.Herein, upon detecting the vehicle is coming to the bottom of a hill andwill soon be going up a hill, the engine controller may restart theengine before the operator presses the accelerator pedal.

At 318, it may be determined whether the engine speed (N_(e)) is above athreshold, for example, above 1000 rpm. If the engine speed has notreached the threshold speed, the engine may continue to be cranked at320 to raise the engine speed to the threshold value. Once the engine isrotating at or above the threshold speed, the routine proceeds to 322wherein engine operation may be initiated, for example, by resuming fuelinjection.

Further, a transmission clutch control operation may be executed toadjust the amount of engine torque transferred to the moving vehiclewheels. Specifically, a degree of engagement of a transmission clutchmay be adjusted to adjust a torque transmitted to the wheel. In oneexample, the engine may be started with the transmission engaged, byengaging a transmission forward clutch or a torque converter lock-upclutch, and then adjusting an amount of clutch slippage responsive to atleast one of an engine speed (at the time of engine restart), a desiredengine speed profile, and a driver demanded torque. In one example, theadjustment may include increasing an amount of clutch slippage when theengine speed is below a threshold, and decreasing an amount of clutchslippage when the engine speed is above the threshold. In anotherexample, adjusting the amount of clutch slippage responsive to enginespeed may include, increasing the amount of slippage as the engine speedincreases, and then reducing the amount of slippage (for example,reducing to provide substantially no slippage) after the engine speedreaches the threshold.

In another example, during the vehicle coasting condition, the enginemay be stopped with the transmission engaged (for example, by engagingthe torque converter lock-up clutch) and with a first, lower, amount oftransmission clutch slippage. Then, during a subsequent restart, theengine may be started, while the vehicle is still moving, with thetransmission still engaged and with a second, larger, amount oftransmission clutch slippage.

In still another example, during the engine shutdown, the transmissionmay be fully disengaged. Then, during a subsequent restart, the enginemay be started with the transmission still disengaged, for example, withthe transmission in a neutral gear. The transmission may then be engagedafter the engine speed has reached a threshold speed. The thresholdengine speed may be determined as a function of the desired transmissiongear, which in turn, may be determined as a function of the acceleratorpedal position input and the vehicle speed. In yet another example, theclutch capacity of the transmission clutches may be controlled totransmit only the desired amount of torque and to spin (due to clutchslippage) at torques above that. For example, the clutch torque capacitymay be adjusted by changing the duty cycle of the clutch pressurecontrolling variable force solenoids. Herein, in addition to controllingthe torque transmitted by the transmission, the clutches may be kept ina pre-stroked condition, thereby reducing delays in clutch engagement.

Example transmission clutch adjustments are further explained hereinwith reference to FIG. 4.

Other engine operating conditions may also be adjusted to enable asmooth restart. For example, fuel timing, position of cams, spark timing(advance/retard), fuel injection location of start of injection, fuelinjection amount, fuel injection pressure, and throttle position may beadjusted to improve the engine start. In one example, fuel may bedirectly injected to a cylinder before engine rotation so as to assistin engine rotation when a spark is output to combust the injected fuel.In another example, the fuel timing may additionally be advanced orretarded relative to a crankshaft angle at which fuel was delivered tothe engine prior to last engine stop. In still another example, athrottle angle may be set so that a controlled amount of air enters thecylinder during the engine restart. Further, combinations orsub-combinations of these and other parameters may be adjusted duringthe engine start.

The engine control parameters may also be set in relation to the vehiclespeed during the engine restart during vehicle moving conditions. Forexample, cam timing, throttle position, fuel start of injection, fueltiming, and spark angle may be adjusted such that the amount of torquegenerated by the engine at restart of the moving vehicle is at orslightly below the torque required to keep the vehicle moving at thepresent vehicle speed. In another example, the engine may be restartedby setting the engine control parameters to a first position at enginerestart, and then shortly after start or during engine run-up, theparameters may be set to a second position that is based on the vehiclespeed. In this way, the operation of the engine can be adjusted inrelation to the vehicle's speed so that smooth transitions betweenoperating the vehicle without the engine and operating the vehicle withthe engine can occur.

Now turning to FIG. 4, map 400 depicts example engine shutdown andrestart scenarios with a plurality of graphs 402-414. Graph 402 depictschanges in vehicle speed during the example vehicle coast engineshutdown and/or restart operations. Graph 404 depicts changes in enginespeed over the same duration. Graph 406 provides an indication of thestatus (0 or 1) of a DFSO operation. Graph 408 provides an indication ofthe absence or presence (0 or 1) of a starter motor assistance. Graph410 depicts changes in torque output. Graph 412 depicts adjustments to atransmission engagement state, as indicated by corresponding changes ina transmission clutch pressure. Graph 414 further depicts changes in anamount of clutch slippage for the transmission clutch of graph 412.

At t₁, a first vehicle moving condition, specifically a vehicle coastingcondition, may be confirmed. Herein, the vehicle operator may haveremoved his foot from the vehicle accelerator pedal and may not havepressed the brake pedal. Further, at the time of driver foot-off fromthe accelerator and brake pedals, the vehicle speed may be a higheramount, for example, the vehicle speed may be above a threshold. Assuch, due to the accelerator pedal and brake pedals not being depressed,the vehicle speed may slowly decrease (depicted in graph 402) as thevehicle coasts towards a potential vehicle stop. In response to thefirst vehicle moving condition, at t₁, an engine controller may beconfigured to shutdown the engine, for example, by performing a DFSOoperation (graph 406) wherein a fuel injection to the engine cylindersis shut off to stop combustion therein. In response to the engineshutdown, the engine speed may start to drop (graph 404).

Further, to aid engine spin-down, the wheel torque of the moving wheelsmay be decoupled from the engine by at least partially disengaging thetransmission. In one example, this may be achieved by at least partiallydisengaging a transmission clutch. In one example, the transmissionclutch may be a torque converter lock-up clutch and the clutch may bedisengaged (for example, partially disengaged or completely disengaged)by reducing the clutch pressure, as indicated in graph 412. In analternate example, the transmission clutch may be a forward clutch. Inone example, in addition to reducing the engagement of the transmissionclutch, the clutch may be slipped, for example by a first amount 418 ofclutch slippage (graph 414). The transmission clutch may then bemaintained in the reduced engagement state with the first amount ofclutch slippage until a subsequent engine restart is requested.

At t₂, a second vehicle moving condition, specifically an engine restartwhile the vehicle is moving condition, may be confirmed. For example,the engine may be restarted in response to the vehicle operator applyinghis foot on the vehicle accelerator pedal (or brake pedal). In anotherexample, the engine may be restarted in response to the vehicle speedbeing a lower amount, for example, below a threshold. In response to thesecond vehicle moving condition, at t₂, the engine controller may beconfigured to restart the engine, for example, by stopping the DFSOoperation (graph 406) and resuming fuel injection to the enginecylinders to start combustion therein. Additionally, the enginecontroller may start cranking the engine with starter motor assistance(graph 408). In response to the engine restart, the engine speed maystart to rise (graph 404).

Further, to enable the driver demanded torque to be provided, and reducea torque surge due to the addition of the engine torque to the wheeltorque, the engine may be restarted while the vehicle is moving with thetransmission still engaged and with the transmission clutch providing asecond, larger, amount 420 of clutch slippage (graph 414). Herein, thetransmission clutch may be controlled, for example using slip control,to provide only the desired amount of torque, and to spin at torquesabove that. The transmission clutch may continue to be maintained in theengaged state with the clutch slipping until the engine speed reaches athreshold. The controller may be configured to reduce the clutchslippage, for example, reduce clutch slippage to provide substantiallyno clutch slippage, when the engine reaches the threshold.

In this way, while the vehicle is moving, an engine shutdown may beperformed and an engine spin-down may be assisted by reducing theeffects of wheel torque from the moving wheels on the engine. Further,by slipping the transmission clutch and adjusting the amount of clutchslippage during a subsequent restart, when the vehicle is still moving,the amount of engine torque transferred from the rotating engine to themoving wheels may be limited during the start. Then, when a higher wheeltorque is desired to keep propelling the vehicle, the amount of slippagemay be reduced to transmit the engine torque to the wheels. By limitingthe amount of engine torque transferred during the start, torque surgeand vehicle lurch may be reduced, and a smooth transition betweencombusting and non-combusting engine modes, while the vehicle is moving,may be achieved.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for controlling a vehicle engine coupled to astepped-gear-ratio transmission, comprising: in response to a firstvehicle moving condition, shutting down the engine and at leastpartially disengaging the transmission while the vehicle is moving; andduring a subsequent restart, while the vehicle is moving, starting theengine using starter motor assistance and adjusting a degree ofengagement of a transmission clutch to adjust a torque transmitted to awheel of the vehicle.
 2. The method of claim 1, wherein the firstvehicle moving condition includes a vehicle accelerator pedal and brakepedal not being pressed, and a vehicle speed being above a threshold. 3.The method of claim 1, wherein the transmission clutch is one of atorque converter lock-up clutch and a forward clutch.
 4. The method ofclaim 1, wherein adjusting a degree of engagement of the transmissionclutch during the restart includes, engaging the clutch and adjusting anamount of clutch slippage, the amount of clutch slippage adjustedresponsive to at least one of an engine speed and a driver demandedtorque.
 5. The method of claim 4, wherein adjusting the amount of clutchslippage responsive to speed includes, increasing an amount of clutchslippage when the engine speed is below a threshold and decreasing anamount of clutch slip when the engine speed is above the threshold. 6.The method of claim 1 further comprising, in response to a secondvehicle moving condition wherein the vehicle is moving with a vehicleaccelerator pedal and brake pedal not pressed, and with a vehicle speedbelow a threshold, not shutting down the engine.
 7. The method of claim1, wherein shutting down the engine includes shutting off a fuel supplyto the engine. 8-21. (canceled)